1. Field of the Invention
The present invention relates to a flash control device that controls a plurality of flash devices in synchronization with a photographing operation of a camera.
In addition, the present invention relates to a flash control system that performs a multiple-flash operation with a plurality of flash devices.
Moreover, the present invention relates to a master flash device that gives light emission indication to a remote flash device.
Furthermore, the present invention relates to a remote flash device that receives the light emission indication from the master flash device.
2. Description of the Related Art
As a device that controls a plurality of flash devices (hereinafter referred to as SB), for example, Japanese Unexamined Patent Application Publication No. 2000-89306 (hereinafter referred to as patent document 1) is known.
In addition, a system disclosed in Japanese Patent No. 3262874 (hereinafter referred to as patent document 2) is known.
FIG. 34(a) and FIG. 34(b) are schematic diagrams describing timings of light emissions of those conventional examples.
In the patent document 1, as shown in FIG. 34(a), a pulse light emission of a master SB causes a slave SB to prepare to emit light. Thereafter, when the slave SB detects a main light emission of the master SB, the slave SB performs a light emission in synchronization with the main light emission.
In this case, since the master SB communicates with the slave SB using pulse light emitted by a xenon lamp, the communication is performed before the shutter of the camera is released, to prevent a photographing operation of the camera from being adversely affected by the pulse light.
In contrast, in the patent document 2, as shown in FIG. 34(b), with a pulse light emission performed by a camera (master SB), a timing T of the light emission is sent to a slave SB. The slave SB counts the timing T of the light emission with its timer and performs a main light emission by its own decision.
As a photographing technology of a camera, multiple flashing is known. In the multiple flashing, to adjust the shadow of a subject and to increase the light amount, a plurality of flash devices emits light. In this case, it is preferable that the plurality of flash devices emits light at the same time. If flashing timings of the flash devices are different, the photographed image will blur when a moving subject is photographed.
In the system described in the patent document 1 (see FIG. 34(a)), immediately after the slave SB receives a light emission from the master SB, it performs a light emission. Thus, the patent document 1 is superior to the other in simultaneity.
In addition, as a photographing technique of a camera, rear synchronous photography (rear curtain synchronous photography) is known. In this technique, a main light emission is performed immediately before the shutter is closed. In the rear synchronous photography, the trace of a subject that has not been flashed overlaps with the subject that has been clearly flashed. Thus, the trace of the moving subject can be photographed as a tail.
In the rear synchronous photography, to photograph a long trace of a moving subject, the time period until a light emission is performed after the shutter is released may become long. In this case, in the patent document 1, since the slave SB prepares to perform a light emission by a communication from the master SB before the shutter is released, the waiting time of the slave SB becomes long. Consequently, the slave SB on standby tends to react with light emitted by other source than the master SB and malfunction.
When a subject is photographed with a background of fireworks by the rear synchronous photography, in a moment that the fireworks light, the slave SB reacts thereto and emits light. In this case, the slave SB cannot emit light at the expected timing of the rear synchronous photography. Furthermore, the slave SB fails to emit light in synchronization with the master SB.
To prevent such problems, if pulse communication is tried to perform immediately before light is emitted by the rear synchronous photography, the pulse light is photographed by the camera. As a result, a proper exposure cannot be obtained.
In such a case, the technology in the patent document 2 (see FIG. 34(b)) is effective. In this system, the timing of a light emission to be performed by the slave SB can be indicated in advance. Thus, even in a case where it takes time until the slave SB actually emits light after it receives a communication, the timing of the light emission that the slave SB performs can be indicated with its own timer.
However, in such a system, if there is a difference between the timer of the camera side and that of the slave SB side, the timings of the light emissions of the camera side and the slave SB side deviate. In particular, when the rear synchronous photography is performed, the time period until the slave SB actually emits light after it receives a communication may become endlessly long. For example, even if the error of the timer is 1%, a shutter time of 100 seconds results in a deviation of one second in the timing of a light emission.